Channel coherence time describes the time duration during which characteristics of a wireless channel do not vary. Knowledge of the channel coherence time or the detection of a sudden change in the channel state may be used to improve the efficiency of several functions in a wireless system. Indeed, the length of the aggregated packets is usually less than the channel coherence time to ensure that data are successfully exchanged (transmitted and/or received) between wireless client devices and access points.
Mobility of the wireless client devices is another factor which reduces the channel coherence time. Therefore, when a wireless client device is mobile relative to the access points, a minimal packet aggregation length suitable for all velocities, or no aggregation at all, is used to ensure proper/successful data exchanges.